McMurry Organic Chemistry 6th edition Chap 2 Substitution Reactions of Benzene and Its Derivatives  Benzene is aromatic: a cyclic conjugated compound with 6 π electrons  Reactions of benzene lead to the retention of the aromatic core  Electrophilic aromatic substitution replaces a proton on benzene with another electrophile

McMurry Organic Chemistry 6th edition Chap 3 16.1 Bromination of Aromatic Rings  Benzene’s π electrons participate as a Lewis base in reactions with Lewis acids  The product is formed by loss of a proton, which is replaced by bromine  FeBr 3 is added as a catalyst to polarize the bromine reagent

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McMurry Organic Chemistry 6th edition Chap 4 Addition Intermediate in Bromination  The addition of bromine occurs in two steps  In the first step the π electrons act as a nucleophile toward Br 2 (in a complex with FeBr 3 )  This forms a cationic addition intermediate from benzene and a bromine cation  The intermediate is not aromatic and therefore high in energy (see Figure 16.2)

McMurry Organic Chemistry 6th edition Chap 6 16.2 Other Aromatic Substitutions  The reaction with bromine involves a mechanism that is similar to many other reactions of benzene with electrophiles  The cationic intermediate was first proposed by G. W. Wheland of the University of Chicago and is often called the Wheland intermediate George Willard Wheland 1907-1974

McMurry Organic Chemistry 6th edition Chap 7 Aromatic Chlorination and Iodination  Chlorine and iodine (but not fluorine, which is too reactive) can produce aromatic substitution with the addition of other reagents to promote the reaction  Chlorination requires FeCl 3  Iodine must be oxidized to form a more powerful I + species (with Cu + or peroxide)

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